The overarching goal of this investigation is to understand the mechanism(s) whereby the tachykinin neuropeptide, substance P (SP), and its preferred receptor, Neurokinin-lR (NK1R) modulate the immunopathogenesis of HIV as central mediators in the interaction between the immune and nervous systems. Our major hypothesis is that altered SP and NK1R, are mechanistically important in HIV pathogenesis and that this receptor and its ligand are altered in association with neurocognitive changes and life stress and depression in HIV-infected individuals. We showed that the non-peptide SP antagonist (CP-96,345) inhibits HIV replication in human mononuclear phagocytes through down-regulation of CCR5, the chemokine receptor, the principal co-receptor for HIV entry into macrophages and also by NK1R antagonist inhibition of endogenous SP production. The SP autocrine loop has an important role in regulating cytokine and inflammatory responses. HIV reciprocally enhances SP expression in human immune cells, eliciting a feed-forward cycle. We discovered that cell differentiation in vitro from monocyte to macrophage phenotype (THP cells) results in the expression of both the NK1R-T (truncated) and NK1R-F (full-length), whereas the monocyte cell expresses only NK1R-T. The qualitative and quantitative expression of NK1R and its truncated (NK1R-T) and full length forms (NK1R-F) have functional consequences for calcium flux in macrophages. In the brain cingulate cortex, mRNA expression of both the NK1R-T and NK1R-F are reduced in HIV-infected subjects. We will use cells from both the immune and the CNS systems, including peripheral monocyte-macrophages and cells obtained from select human brain regions to examine these mechanisms. We will examine the cell biology of the interaction between NK1R (NK1R-F and NK1R-T) and HIV and chemokine receptors. Our aims are: (1) To investigate expression of NK-1RF in monocyte-derived macrophages and their associations with CCR5, CD4, Fractalkine, and IL-8. (2) We will investigate the physical and functional interactions between NK1R-T, NK1R-F receptors and CCR5. (3) We will explore the role of cytosolic Ca2+ increase in the cross-talk between NK1R-F, NK1R-T, and CCR5. (4) We hypothesize that altered levels of either or both NK1R-T or NK1R-F mRNA and protein, or receptor function, are associated with alterations with cognitive function in HIV-1/AIDS infected individuals, and these effects alter CCR5-NK1R interaction. Relevance to Public Health: These studies will further lead to understanding the pathogenesis of neurocognitive changes in HIV disease and lead to unique and novel therapeutic intervention.